Behavior of Cr(VI) removal from wastewater by adsorption onto HCl activated Akadama clay

• Al and Fe functional groups on Akadama clay increased after acid activation.
• Wide pH ranges of 3–9 were found to be suitable for Cr(VI) adsorption onto HCl-AC.
• The Cr(VI) adsorption process followed the pseudo-second-order kinetic model.
• The adsorption data fitted well to the Freundlich isotherm model.
• HCl-AC could effectively remove Cr(VI) from practical wastewater.

Clay minerals are affordable adsorbents for the removal of industrial contaminants. In this study, HCl was selected as an effective acid modifier to activate pristine Akadama clay (AC) and batch adsorption experiments were conducted to evaluate the Cr(VI) adsorption performance onto HCl activated Akadama clay (HCl-AC). After activation, the optimum application pH was broadened from 2 to 3–9. The experimental data best fitted the pseudo-second-order model. The Freundlich isotherm and Dubinin–Radushkevich isotherm were found to fit the data better than the Langmuir isotherm, revealing heterogeneous adsorption occurred onto HCl-AC. XPS analysis and desorption experiments proved that ligand exchange as well as electronic attraction contributed more than reduction process during the adsorption of Cr(VI) onto HCl-AC. The HCl-AC developed in the present study, with 98.9% of Cr(VI) removal from tannery wastewater, could be an attractive and competitive adsorbent in practice.